This section provides background information related to the present disclosure which is not necessarily prior art.
The field of environmental analysis has long known about the technique of exposing so-called passive samplers over a long period of time in the water of a body of water, in order that certain organic and inorganic pollutant compounds relevant to the quality of the water in the body of water are accumulated in the passive samplers. Subsequently, the accumulated quantity of the compounds in question can be extracted, and a time-averaged concentration of the pollutants in solution can be determined, in order to thus arrive at a determination concerning the pollution of the body of water. Such passive samplers are known for example from GB 1 566 253 A. However, there are also other passive samplers, such as the so-called Chemcatcher Metal sampler or the DGT sampler for example, which are used for the accumulation of inorganic pollutants.
Such passive samplers are designed to comprise a collection phase having high affinity for the target analytes, and this collection phase is usually separated from the water phase by a membrane, which forms the active surface section. The other surfaces of the sampler do not allow the substances in question to pass through them.
In principle, for their exposure, these passive samplers may be placed directly into the body of water arranged in special cages or supports, allowing the water there to move around them. However, the problem with this is that when the sampler remains in the body of water for a sufficiently long period of time, vegetation or other deposits build up on the active surface section, which results in decreased diffusion of the substances in question into the inside of the sampler in the collection phase. When the total quantity of the substances in question accumulated in the sampler is subsequently determined in order to thus also arrive at a determination concerning the pollution of the body of water, the deposits and the vegetation cause the pollution to be underestimated.
Another problem with this type of arrangement of the passive samplers directly in the body of water is the lack of information about the flow conditions at the flat active surface section. Since it is precisely this streaming around the active surface section that determines the degree of diffusion of the substances in question into the inside of the passive sampler, this lack of clarity further reduces the precision of the determination concerning the pollution of the body of water.
It is therefore fundamentally desirable for the passive samplers to be arranged in such a way that, on the one hand, there are defined flow conditions in the active surface section zone, and on the other hand, that deposits and vegetation are prevented from building up on the active surface section.
Gunold et al., Calibration of the Chemcatcher passive sampler for monitoring selected polar and semi-polar pesticides and surface water, Environmental Pollution 155 (2008) 52-60, has already described an arrangement not for the actual concentration measurement in the body of water, but rather for calibration under laboratory conditions, in which arrangement passive samplers are arranged on a rotationally driven holder in an open container, through which water containing organic substances is fed at a pre-defined flow rate. However, this setup has the disadvantage that the flow conditions at the active surface section of the passive sampler are still not precisely defined.